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<h1 id="学习一下MyBatis"><a href="#学习一下MyBatis" class="headerlink" title="学习一下MyBatis"></a>学习一下MyBatis</h1><h2 id="1、MyBatis介绍"><a href="#1、MyBatis介绍" class="headerlink" title="1、MyBatis介绍"></a>1、MyBatis介绍</h2><p>Mybatis:    用来和数据库进行交互，持久化层框架(SQL映射框架)；</p>
<p>1)、从原始的JDBC—–&gt;dbutils(QueryRunner)——&gt;JdbcTemplate—–&gt;xxx</p>
<p>​    称为工具；</p>
<p>​    工具：一些功能的简单封装</p>
<p>​    框架：某个领域的整体解决方案；缓存，考虑异常的处理问题，考虑部分字段映射问题…</p>
<p>不使用原生的JDBC：</p>
<p>​    1）、麻烦，有太多重复的代码，高耦合</p>
<p>​    2）、sql语句是硬编码再程序中，耦合（数据库编码与java编码耦合）</p>
<p>2）、Hibernate–数据库交互的框架(ORM框架，Object-Relationl Mapping) 使用各种框架</p>
<p>全自动的持久层框架</p>
<p>JPA也是ORM框架</p>
<p>创建好JavaBean；</p>
<p>通过一个注解直接生成数据库中的表</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Table(&quot;t_employee&quot;)</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Employee</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> Integer empId;</span><br><span class="line">    <span class="keyword">private</span> String empName;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">session.get(<span class="string">&quot;1&quot;</span>,Employee.class);</span><br></pre></td></tr></table></figure>

<p>缺点：</p>
<p>​    1）、定制sql；比较麻烦</p>
<p>​    2）、HQL；Hibernate Query Language</p>
<p>​    3）、全映射框架，部分字段映射很难；能做，但是数据库开销很大，取一个字段要把整个表的全取出</p>
<p>希望：最好有一个框架能支持定制化sql，而且还功能强大；sql也不要硬编码在Java文件中（导致维护麻烦）</p>
<p>MyBatis应运而生，将SQL语句全部写在配置文件中，自动执行，因业务的变更只用更改配置文件的SQL语句，而不需要更改Java代码，或者修改的代码很少</p>
<p>特点：</p>
<p>​    1）、MyBatis将重要的步骤抽取出来可以人工定制，其他步骤自动化；</p>
<p>​    2）、重要步骤都是写在配置文件，便于维护；</p>
<p>​    3）、完全解决数据库的优化问题；</p>
<p>​    4）、MyBatis底层就是对原生JDBC的一个简单封装；</p>
<p>​    5）、即将Java编码与SQL抽取了出来，还不会失去自动化功能；半自动化的持久化层框架</p>
<p>​    6）、是一个轻量级框架</p>
<p>sql与java编码分开，功能边界清晰，一个专注业务，一个专注于数据</p>
<h2 id="2、HelloWorld"><a href="#2、HelloWorld" class="headerlink" title="2、HelloWorld"></a>2、HelloWorld</h2><p>MyBatis是持久化层框架(SQL映射框架)-操作数据库</p>
<p>1）、环境搭建</p>
<p>​    1）、创建一个maven工程；</p>
<p>​    2）、创建测试库、测试表、以及封装数据的JavaBean，和操作数据的dao</p>
<p>​        创建表:</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">CREATE</span> <span class="keyword">TABLE</span> <span class="string">`t_employee`</span> (</span><br><span class="line">  <span class="string">`id`</span> <span class="built_in">int</span>(<span class="number">11</span>) <span class="keyword">NOT</span> <span class="literal">NULL</span> AUTO_INCREMENT,</span><br><span class="line">  <span class="string">`empname`</span> <span class="built_in">varchar</span>(<span class="number">50</span>) <span class="keyword">COLLATE</span> utf8mb4_bin <span class="keyword">NOT</span> <span class="literal">NULL</span>,</span><br><span class="line">  <span class="string">`gender`</span> <span class="built_in">int</span>(<span class="number">1</span>) <span class="keyword">DEFAULT</span> <span class="literal">NULL</span>,</span><br><span class="line">  <span class="string">`email`</span> <span class="built_in">varchar</span>(<span class="number">100</span>) <span class="keyword">COLLATE</span> utf8mb4_bin <span class="keyword">DEFAULT</span> <span class="literal">NULL</span>,</span><br><span class="line">  PRIMARY <span class="keyword">KEY</span> (<span class="string">`id`</span>)</span><br><span class="line">)</span><br></pre></td></tr></table></figure>

<p>​        创建javabean：Employee（封装表的数据）</p>
<p>​        创建一个Dao接口，用来操作数据库</p>
<p>​    3）、用MyBatis操作数据库</p>
<p>​        1）、导包，使用maven导入相应依赖即可</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">&lt;!--引入mybatis--&gt;</span></span><br><span class="line">      <span class="comment">&lt;!-- https://mvnrepository.com/artifact/org.mybatis/mybatis --&gt;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">dependency</span>&gt;</span></span><br><span class="line">          <span class="tag">&lt;<span class="name">groupId</span>&gt;</span>org.mybatis<span class="tag">&lt;/<span class="name">groupId</span>&gt;</span></span><br><span class="line">          <span class="tag">&lt;<span class="name">artifactId</span>&gt;</span>mybatis<span class="tag">&lt;/<span class="name">artifactId</span>&gt;</span></span><br><span class="line">          <span class="tag">&lt;<span class="name">version</span>&gt;</span>3.4.6<span class="tag">&lt;/<span class="name">version</span>&gt;</span></span><br><span class="line">      <span class="tag">&lt;/<span class="name">dependency</span>&gt;</span></span><br><span class="line">      <span class="comment">&lt;!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java --&gt;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">dependency</span>&gt;</span></span><br><span class="line">          <span class="tag">&lt;<span class="name">groupId</span>&gt;</span>mysql<span class="tag">&lt;/<span class="name">groupId</span>&gt;</span></span><br><span class="line">          <span class="tag">&lt;<span class="name">artifactId</span>&gt;</span>mysql-connector-java<span class="tag">&lt;/<span class="name">artifactId</span>&gt;</span></span><br><span class="line">          <span class="tag">&lt;<span class="name">version</span>&gt;</span>5.1.49<span class="tag">&lt;/<span class="name">version</span>&gt;</span></span><br><span class="line">      <span class="tag">&lt;/<span class="name">dependency</span>&gt;</span></span><br></pre></td></tr></table></figure>



<p>​        2）、写配置（两个，全局配置文件（知道mybatis运行的），dao接口的实现文件（描述dao中每个方法怎么工作））</p>
<p>​                1）、第一个配置文件：称为mybatis的全局配置文件，指导mybatis如何正确运行，比如连接哪个数据库</p>
<p>在配置文件mybatis-config.xml中即可完成</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot; ?&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">configuration</span></span></span><br><span class="line"><span class="meta">        <span class="meta-keyword">PUBLIC</span> <span class="meta-string">&quot;-//mybatis.org//DTD Config 3.0//EN&quot;</span></span></span><br><span class="line"><span class="meta">        <span class="meta-string">&quot;http://mybatis.org/dtd/mybatis-3-config.dtd&quot;</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">configuration</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">environments</span> <span class="attr">default</span>=<span class="string">&quot;development&quot;</span>&gt;</span></span><br><span class="line">        <span class="tag">&lt;<span class="name">environment</span> <span class="attr">id</span>=<span class="string">&quot;development&quot;</span>&gt;</span></span><br><span class="line">            <span class="tag">&lt;<span class="name">transactionManager</span> <span class="attr">type</span>=<span class="string">&quot;JDBC&quot;</span>/&gt;</span></span><br><span class="line">            <span class="comment">&lt;!-- 配置连接池 --&gt;</span></span><br><span class="line">            <span class="tag">&lt;<span class="name">dataSource</span> <span class="attr">type</span>=<span class="string">&quot;POOLED&quot;</span>&gt;</span></span><br><span class="line">                <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;driver&quot;</span> <span class="attr">value</span>=<span class="string">&quot;com.mysql.jdbc.Driver&quot;</span>/&gt;</span></span><br><span class="line">                <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;url&quot;</span> <span class="attr">value</span>=<span class="string">&quot;jdbc:mysql://localhost:3306/mybatis?useUnicode=true<span class="symbol">&amp;amp;</span>characterEncoding=UTF-8<span class="symbol">&amp;amp;</span>serverTimezone=UTC<span class="symbol">&amp;amp;</span>useSSL=false&quot;</span>/&gt;</span></span><br><span class="line">                <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;username&quot;</span> <span class="attr">value</span>=<span class="string">&quot;root&quot;</span>/&gt;</span></span><br><span class="line">                <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;password&quot;</span> <span class="attr">value</span>=<span class="string">&quot;root&quot;</span>/&gt;</span></span><br><span class="line">            <span class="tag">&lt;/<span class="name">dataSource</span>&gt;</span></span><br><span class="line">        <span class="tag">&lt;/<span class="name">environment</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">environments</span>&gt;</span></span><br><span class="line"></span><br><span class="line">    <span class="tag">&lt;<span class="name">mappers</span>&gt;</span></span><br><span class="line">        <span class="tag">&lt;<span class="name">mapper</span> <span class="attr">resource</span>=<span class="string">&quot;org/mybatis/example/BlogMapper.xml&quot;</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">mappers</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">configuration</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>​            2）、第二个配置文件：（编写每一个方法都如歌向数据库发送sql语句，如何执行…,相当于接口的实现类）EmployeeDao.xml</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">&lt;!-- namespace:命名空间；写接口的全类名，相当于告诉MyBatis这个配置文件时实现哪个接口的--&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">mapper</span> <span class="attr">namespace</span>=<span class="string">&quot;com.hch.dao.EmployeeDao&quot;</span>&gt;</span></span><br><span class="line">    <span class="comment">&lt;!--定义一个查询操作: select定义一个查询操作， id：方法名，相当于这个配置是对某个方法的实现</span></span><br><span class="line"><span class="comment">    resultType:指定方法运行后的返回值类型(查询操作必须指定)</span></span><br><span class="line"><span class="comment">    #&#123;id&#125;:代表取出 传递过来的某个参数的值</span></span><br><span class="line"><span class="comment">    --&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">select</span> <span class="attr">id</span>=<span class="string">&quot;getEmployee&quot;</span> <span class="attr">resultType</span>=<span class="string">&quot;com.hch.Employee&quot;</span>&gt;</span></span><br><span class="line">    select * from t_employee where id = #&#123;id&#125;</span><br><span class="line">    <span class="tag">&lt;/<span class="name">select</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">mapper</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>​            3）、我们写的dao接口的实现文件，mybatis默认是不知道的，需要在<strong>全局配置文件mybatis-config.xml</strong>中注册</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">&lt;!--引入我们自己编写的每一个接口的实现文件--&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">mappers</span>&gt;</span></span><br><span class="line">        <span class="comment">&lt;!--resource：表示从类路径下找资源--&gt;</span></span><br><span class="line">        <span class="tag">&lt;<span class="name">mapper</span> <span class="attr">resource</span>=<span class="string">&quot;config/EmployeeDao.xml&quot;</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">mappers</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>​        3）、测试</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> com.hch.bean.Employee;</span><br><span class="line"><span class="keyword">import</span> com.hch.dao.EmployeeDao;</span><br><span class="line"><span class="keyword">import</span> org.apache.ibatis.io.Resources;</span><br><span class="line"><span class="keyword">import</span> org.apache.ibatis.session.SqlSession;</span><br><span class="line"><span class="keyword">import</span> org.apache.ibatis.session.SqlSessionFactory;</span><br><span class="line"><span class="keyword">import</span> org.apache.ibatis.session.SqlSessionFactoryBuilder;</span><br><span class="line"><span class="keyword">import</span> org.junit.Test;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> java.io.IOException;</span><br><span class="line"><span class="keyword">import</span> java.io.InputStream;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyBatisTest</span> </span>&#123;</span><br><span class="line">    <span class="meta">@Test</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">test</span><span class="params">()</span> <span class="keyword">throws</span> IOException </span>&#123;</span><br><span class="line">        <span class="comment">//1、根据全局配置文件，创建出一个SqlSessionFactory</span></span><br><span class="line">        <span class="comment">//SqlSessionFactory：是SqlSession工厂，负责创建SqlSession对象</span></span><br><span class="line">        <span class="comment">//SqlSession：sql会话（代表和数据库的一次会话）</span></span><br><span class="line">        String resource = <span class="string">&quot;mybatis-config.xml&quot;</span>;</span><br><span class="line">        InputStream inputStream = Resources.getResourceAsStream(resource);</span><br><span class="line">        SqlSessionFactory sqlSessionFactory = <span class="keyword">new</span> SqlSessionFactoryBuilder().build(inputStream);</span><br><span class="line">        Employee employee = <span class="keyword">null</span>;</span><br><span class="line">        SqlSession session =<span class="keyword">null</span>;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="comment">//2、获取和数据库的一次会话</span></span><br><span class="line">            session = sqlSessionFactory.openSession();</span><br><span class="line">            <span class="comment">//3、使用SqlSession操作数据库,获取到dao接口的实现</span></span><br><span class="line">            EmployeeDao employeeDao = session.getMapper(EmployeeDao.class);</span><br><span class="line">            <span class="comment">//调用接口中定义的方法</span></span><br><span class="line">            employee = employeeDao.getEmpById(<span class="number">1</span>);</span><br><span class="line">            System.out.println(employee);</span><br><span class="line">        &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line">            e.printStackTrace();</span><br><span class="line">        &#125;<span class="keyword">finally</span> &#123;</span><br><span class="line">            session.close();</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>​            测试结果：</p>
<p><img src="http://s1.wailian.download/2020/04/30/mybatis_helloworld.png" alt="mybatis_helloworld.png"></p>

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